1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.functor.core.composite;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.functor.BinaryFunction;
22 import org.apache.commons.lang3.Validate;
23
24 /**
25 * Transposes (swaps) the arguments to some other
26 * {@link BinaryFunction function}.
27 * For example, given a function <i>f</i>
28 * and the ordered pair of arguments <i>a</i>,
29 * <i>b</i>.
30 * {@link #evaluate evaluates} to
31 * <code>f.evaluate(b,a)</code>.
32 * <p>
33 * Note that although this class implements
34 * {@link Serializable}, a given instance will
35 * only be truly <code>Serializable</code> if the
36 * underlying functor is. Attempts to serialize
37 * an instance whose delegate is not
38 * <code>Serializable</code> will result in an exception.
39 * </p>
40 *
41 * @param <L> the left argument type.
42 * @param <R> the right argument type.
43 * @param <T> the returned value type.
44 * @version $Revision: 1365329 $ $Date: 2012-07-24 19:34:23 -0300 (Tue, 24 Jul 2012) $
45 */
46 public class TransposedFunction<L, R, T> implements BinaryFunction<L, R, T>, Serializable {
47 /**
48 * serialVersionUID declaration.
49 */
50 private static final long serialVersionUID = -5824252875453493940L;
51 // attributes
52 // ------------------------------------------------------------------------
53 /**
54 * The adapted function.
55 */
56 private final BinaryFunction<? super R, ? super L, ? extends T> function;
57
58 // constructor
59 // ------------------------------------------------------------------------
60 /**
61 * Create a new TransposedFunction.
62 * @param function BinaryFunction to transpose.
63 */
64 public TransposedFunction(BinaryFunction<? super R, ? super L, ? extends T> function) {
65 this.function = Validate.notNull(function, "BinaryFunction argument was null");
66 }
67
68 // functor interface
69 // ------------------------------------------------------------------------
70 /**
71 * {@inheritDoc}
72 */
73 public final T evaluate(L left, R right) {
74 return function.evaluate(right, left);
75 }
76
77 /**
78 * {@inheritDoc}
79 */
80 @Override
81 public final boolean equals(Object that) {
82 return that == this || (that instanceof TransposedFunction<?, ?, ?>
83 && equals((TransposedFunction<?, ?, ?>) that));
84 }
85
86 /**
87 * Learn whether another TransposedFunction is equal to this.
88 * @param that TransposedFunction to test
89 * @return boolean
90 */
91 public final boolean equals(TransposedFunction<?, ?, ?> that) {
92 return null != that && function.equals(that.function);
93 }
94
95 /**
96 * {@inheritDoc}
97 */
98 @Override
99 public int hashCode() {
100 int hash = "TransposedFunction".hashCode();
101 hash ^= function.hashCode();
102 return hash;
103 }
104
105 /**
106 * {@inheritDoc}
107 */
108 @Override
109 public String toString() {
110 return "TransposedFunction<" + function + ">";
111 }
112
113 // static
114 // ------------------------------------------------------------------------
115 /**
116 * Transpose a BinaryFunction.
117 * @param <L> the left argument type.
118 * @param <R> the right argument type.
119 * @param <T> the returned value type.
120 * @param f BinaryFunction to transpose
121 * @return TransposedFunction
122 */
123 public static <L, R, T> TransposedFunction<R, L, T> transpose(BinaryFunction<? super L, ? super R, ? extends T> f) {
124 return null == f ? null : new TransposedFunction<R, L, T>(f);
125 }
126
127 }